GROWTH AND AMINO ACID UTILISATION IN BROILER CHICKENS FED SUPPLEMENTAL GLYCINE IN LOW CRUDE PROTEIN DIETS WITH VARIED METHIONINE AND THREONINE

Abstract

Limiting Amino Acid (AA) fortification such as methionine and threonine of vegetable based low Crude Protein (CP) diets for broiler chicks is often adopted for decreasing production cost and nitrogen emission but could impact negatively on growth of broiler chickens. Supplemental glycine could improve broiler chicken performance when low CP diets are fed. However, information on the quantification of the sparing effect of glycine for methionine and threonine in low CP diets is scanty. Therefore, the impact of supplemental glycine on performance and AA utilisation of broiler chicken (21 days) offered low CP diets with varying methionine and threonine concentrations were investigated. Nine diets were formulated to contain 22, 20 and 18% CP levels each in combination with supplemental glycine at 0.0, 0.2 and 0.4% inclusion. One-day old Arbor Acre chicks (n=288) were randomly allotted to the diets in a 3×3 factorial arrangement with four replicates of eight birds/replicate. Fifteen diets containing 0.3, 0.5 and 0.7% methionine levels each having 0.2, 0.4, 0.6, 0.8 and 1.0% glycine were formulated. Another 15 diets were formulated containing 0.7, 0.8, and 0.9% threonine, each in combination with 0.2, 0.4, 0.6, 0.8 and 1.0% supplemental glycine. One-day old Cobb-vantress chicks (n=1275) were randomly distributed to the 15 diets each in a 3×5 factorial arrangements with five replications of 17 birds/replicate. Average Daily Gain-AWG (g), Feed Conversion Ratio-FCR, Average Breast Weight-ABW (g/kg) and Abdominal Fat-AF (g/kg) were measured; Apparent Ileal AA Digestibility-AIAAD, Serum Uric Acid-SUA (mg/dL) and Pectoral Muscle Creatine-PMC (mg/g) were assayed. Data were analysed using descriptive statistics, polynomial regression and ANOVA at α0.05. A significant interaction between CP and glycine levels was recorded on AWG, FCR, AIAAD and AF. Reducing CP levels from 22 to 18% with 0.4% glycine addition significantly improved AWG (31.64±0.97), FCR (1.51±0.12), AIAAD (77.67±4.62%) and reduced AF (13.67±2.87). FCR and ABW of the birds showed a significant interaction between methionine and glycine levels. Linear effect (R²=0.88) of increasing glycine levels was recorded for 0.30% methionine, whereas a quadratic effect was observed for 0.5% (R²=0.92) and 0.7% (R2=0.90) methionine diet on FCR and ABW. Increasing levels of glycine resulted in quadratic response on FCR (1.33±0.06; R²=0.88), ABW (150.30±7.83; R2=0.89) and PMC (3.43±0.38; R2=0.85) with an estimated optimum point at 0.80% glycine. Significant interaction was observed between the glycine and threonine levels on FCR and SUA. With increased glycine levels, FCR improved linearly for 0.7% (R²=0.96) and 0.8% (R²=0.93) threonine diets but quadratically for 0.9% (R²=0.97) threonine diets, with optimum point estimated at 0.8% glycine (1.43±0.03). Decreased linear response of SUA with increasing levels of glycine was observed and lowest concentration recorded for the 0.7% threonine and 1.0% glycine diet (3.43±0.67mg/dL). Also, improved linear (R²=0.88) response of glycine levels were observed for ABW while a quadratic effect was recorded for AWG (842.12±43.13; R²=0.96), FCR (1.43±0.06; R²=0.98) and PMC (3.79±0.41mg/g, R²=0.74) at optimum values of 0.8, 0.8 and 0.6% glycine, respectively. Low dietary crude protein with varying methionine and threonine concentration resulted in optimum performance of broiler chicks at 0.8% glycine level.